      1   1 Identifier i
      1   3 Op_assign
      1   5 Integer 1 
      1   6 Semicolon
      2   1 Keyword_while
      2   7 LeftParen
      2   8 Integer 1 
      2   9 RightParen
      3   3 Identifier i
      3   5 Op_assign
      3   7 Op_subtract
      3   8 Identifier i
      3   9 Semicolon
      4   1 End_of_input
